The present invention generally relates to the processing of highly viscous materials and, more particularly, to an apparatus having a novel and improved stirrer arrangement which integrates a vertical interleaved blade structure with a lateral cross blade structure to provide uniform mixing throughout the vessel and improved processing efficiency.
The highly viscous materials of concern herein generally develop a viscosity in the range of from about 7,500 to about 1,000,000 SSU and greater in the course of processing. The specific nature of the material and its ultimate application are only of concern to the extent that its processing involves the intimate mixing of highly viscous materials as contemplated herein. The highly viscous materials of interest are exemplified by roof coating compositions having an asphalt base and containing an asbestos fiber as well as a glass fiber constituent. In preparing such coating compositions, the components of the composition are typically charged into the mixing apparatus in a timed sequence and particular order, and chemical reactions as well as physical changes may occur during the mixing process. In the case of roof coating compositions, the separate component charges include asphalts, spirits, asbestos fibers, glass fibers and putty fillers. Accordingly, the initial charge to the vessel may include solid and resinous components of widely varying densities as well as liquid components having extremely diverse viscosities and equally diverse dispersing and/or solvency characteristics relative to the solid and resinous components.
For purposes of production efficiency, it is desirable to optimize the vessel or batch capacity to a maximum size with minimization of the processing time. The consistency of the resulting mixed material including uniform blend and/or reaction characteristics and the achievement of uniform viscosity are guidelines in the optimization of the mixing. In many instances, temperature control throughout the mass being mixed is necessary, and it comprises an important processing parameter which also requires a maximum movement of the mass within the apparatus. In the processing of all such highly viscous materials, an important parameter is the apparatus's capability to contend with the required physical manipulation of the mass since relatively high structural loads are imposed by such highly viscous materials. It is also desirable to establish complete mixing action throughout the vessel or batch since the momentum flow of such viscous materials is limited. These optimization considerations have not been heretofore satisfactorily resolved in the prior use of vertically interleaved blade mixers in the processing of highly viscous materials.